What is an antenna?

$A$ carrier wave of peak voltage $12 \, V$ is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of $75 \%$? ...... $V$

Which of the following is the communication channel in case of radio communication?

In the case of amplitude modulation,to avoid distortion,the modulation index $(\mu)$ should be:

The audio signal used to modulate $60 \sin(2\pi \times 10^6 t)$ is $15 \sin(300\pi t)$. The depth of modulation is.......$\%$

The height of a transmitting antenna at the top of a tower is $25 \; m$ and that of the receiving antenna is $49 \; m$. The maximum distance between them for satisfactory communication in $LOS$ (Line of Sight) is $K \sqrt{5} \times 10^{2} \; m$. The value of $K$ is $\dots$ [Assume radius of Earth is $64 \times 10^{5} \; m$] (Calculate up to the nearest integer value).